Electric circuit for central telephone offices



A. ROSA Filed Jan. 50, 1928 -tente d Aug. 6, 1929 PATENT, OFFICE.

AUGUSTO ROSA, OF ROME, ITALY.

ELECTRIC CIRCUIT FOR CENTRAL TELEPHONE OFFICES.

Application filed January 30, 1928, Serial No. 250,586, and in Italy January 31, 1927.

This invention relates to a circuit for automatic exchanges having a calling line finder, or for semi-automatic central offices, or for manually operated central offices requiring a preselection by the operator, wherein the line finders are made to work by means of a relay in common to a certain group of suscribers, this relay being connected to the lines of the subscribers of its group by the intermediary of a coil with two windings for each subscriber. One of the windings of the coil has a very high resistance and one of its ends, which coincides with the end of the second winding, is connected to the first contact of the line finders and the connectors of the subscriber, the said common relay being connected to the other end of the high resistance winding, while the free end of the other winding of the coil is connected to the second contact of the line finders and connectors of the subscriber.

The invention will be more particularly described with reference to the accompanying drawing which shows schematically a circuit according to the invention.

In the drawing, A indicates the telephonic apparatus of the subscriber and V and LN are respectively the line finders and the connectors of the apparatus. B indicates a resistance and E is the relay belonging to the group of subscribers which comprises the apparatus A. D is' the high resistance winding and C the low resistance winding, the coinciding ends of these two windings being connected to the first contact F of the line finders and connectors W and LW, while the other end of the resistance D is connected to the relay E and the other end of the resistance C is connected to the other contact I of the line finders and connectors. G indicates a relay complex and H a time lag relay.

When the subscriber A takes off his receiver a circuit is closed from the battery through the resistance B, the apparatus A, the winding C, the Winding D, the common wire of the relay E to the battery. The relay E causes the line finders W belonging to the subscriber A to work and as soon as one of them has found the subscriber who is calling a circuit is set up from the battery through the resistance B, the apparatus A, the winding C, the first contact F on the line finder, the armature g of the relay G to the battery. The relay G starts working, draws the armature 9 down, kills the line finder and remains thus attracted through the following circuit: from the battery through the resistance B, the apparatus A, the second contact I of the line finder, the armature g of the relay G which is down, referring to the diagram, and back to the battery. At the same time, the contact F and thus all the first contacts on the line finders \V and on the connectors LW of the apparatus A are directly switched onto the battery by the armature g and the relay E is thus deenergized. The relay G therefore remains connected to the contact I by the time lag relay H.

This arrangement ensures the fall of the relay E as this relay will not be traversed by a current until after a second subscriber of the same group has been calling. A second line finder cannot stop on the contact that is engaged, as its relay G would be short-circuited. connectors is connected directly to the battery so that there is no danger of the 9 engaged signal not appearing, and a rotating line finder does not produce any noise when passing over the contacts of a subscriber that is engaged.

The first contact on the The arrangement described and shown in n the drawing is given only by way of example and does in no way limit the scope of the invention whose more essential features are set out in the claims.

WVhat I claim is:

1. An electric circuit for central telephonic oflices, comprising the subscribers circuit, a common control relay for a group of subscribers and a coil with a high resistance and a low resistance winding arranged between the said circuit and the relay, the coinciding ends of the two windings being connected to the first contact of the line finders and connectors of the subscriber, while the other end of the high resistance winding is connected to the common relay and the other end of the low resistance winding is connected to the second contact of the line finders and connectors.

2. An electric circuit for central telephonic ofiices, comprising the subscribers circuit, a common control relay for a group of suhscribers' and a 'coil with two windings arranged between' the said circuit and the f v ...r.. J. p D M relay, the common point-of the two windings being connected directly to the battery when 1 a line finder or connector has stopped on the position of the subscriber to whom the coil corresponds.

In testimony whereof I have aflixed my signaturelr j p a, w v v I nnifs'io ROSA. 

